#include <bits/stdc++.h>
using namespace std;

int main()
{
    vector<int>vec;
    for(int i = 0 ;i  < 100 ; ++i)
        vec.push_back(i);
    cout << vec.size() << endl; //100
    cout << vec.capacity() << endl; //128
    vec.erase(vec.begin()+10,vec.end()); //改变了size，但是并未改变capccity
    cout << vec.size() << endl; //10
    cout << vec.capacity() << endl; //128
    vector<int>(vec).swap(vec);
    cout << vec.size() << endl; //10
    cout << vec.capacity() << endl; //10
    vec.clear(); //clear并未真正释放空间！！！
    cout << vec.size() << endl; //0
    cout << vec.capacity() << endl; //10
    vector<int> (vec).swap(vec); //这才真正释放了空间！！
    cout << vec.size() << endl; //0
    cout << vec.capacity() << endl; //0
    return 0;
}

PS：C++11中已经实现了shink_to_fit函数。实现上述功能。